Generally, a video tape recorder (VTR) includes a tape cassette in which a magnetic tape is wound on reels. Methods for loading a rotary drum assembly of the VTR with the magnetic tape and unloading the magnetic tape from the rotary drum assembly are divided into two main classes. However, in both of the two classes, the magnetic tape is drawn from one reel, and it is taken up by the other reel, guided by tape guide pins during the recording or reproducing operation to record or reproduce signals on or from the magnetic tape. Parts for running and guiding the magnetic tape should be accurate to obtain a well-reproduced picture. Particularly, the tape guide pins are important from the viewpoint of the accurate running of the magnetic tape, since the magnetic tape is guided in contact with the tape guide pins. The quality of the tape guide pin greatly influences the performance of the video tape recorder.
Most of the tape guide pins in present video tape recorders are made of austenitic stainless steel SUS 316. The structure of this material may be partially changed from austenite into pseudo-martensite by working process such as plastic working, cutting and grinding, and the material may become weakly magnetic. Magnetic tape guide pins have a bad effect on video signals on the magnetic tape.
The cylindrical surface of a ground and super-finished tape guide pin has microscopically peaked or pointed roughness or unevenness. These microscopic peaks or points of roughness can be smashed or squashed when the cylindrical surface of the tape guide pin is further burnished. Moreover, the hardness of the tape guide pin cannot be significantly increased owing to the magnetism of the material of the pin. The Vickers hardness of the tape guide pin is usually within the range of 280 to 380 Hv; thus, the pin is rather soft.
Accordingly, there is the risk that the back surface of the magnetic tape or the magnetic film thereof maybe damaged or scratched by the above described tape guide pin on which the magnetic tape slides. The life of the magnetic tape in such event would be shortened.